1. Field of the Invention
The present invention relates to an AC generator provided with an inverter. More particularly, the invention relates to an inverter type AC generator that converts a DC output from a DC power source generating unit, which can generate DC power from any energy other than electricity, into an AC output of a certain frequency and is capable of supplying the AC output to a load via an output line.
2. Description of the Related Art
Japanese Publication No. JP-A-S62-77833 illustrates a conventional AC coupling system, in which an electric power converter converts DC power from a DC power source into AC power, which can be connected to an electric power system via a switch. The AC coupling system is designed to allow a synchronization detection circuit to detect an AC voltage of the electric power system and to compare the phase of such AC voltage with a phase of a coupling-point detected voltage on the AC converter side. If both voltage phases match, the AC coupling system is designed to output an operation signal to the switch via a switch operation circuit, thereby turning the switch on. The electric power converter is designed to be driven in synchronization with an AC voltage of the electric power system via a PLL circuit having a phase reference signal and a voltage control circuit.
However, the AC/DC electric power converter described above only controls the voltage phase on its side to match the voltage phase of the electric power system. When both AC output frequencies, including cycles, are mismatched, a high-quality AC output waveform cannot be provided. In addition, since the electric power converter starts the automatic control of the voltage phase at the time the switch is turned on, the phases may not match at an instant when the automatic control starts. In such a case, overcurrent flows-in toward the electric power converter as cross-current via a connecting portion with the electric power system. This may generate an arc in the connecting portion, as well as lead to deficiencies due to heat breakage or deterioration over time.